37 Java Interview Questions
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The document lists 37 practice interview questions about Java programming concepts including questions about String, StringBuffer, and StringBuilder; setting the classpath; differences between final, finalize, and finally; garbage collection; exceptions; floating point equality; enumerations; threads; and collections like ArrayList and LinkedList. It encourages checking answers and offers to schedule a mock interview to help prepare for a Java developer interview.
![What is the problem with this code:
Question 8:
final byte[] bytes = someString.getBytes();](https://image.slidesharecdn.com/37-java-interview-questions-160126092321/85/37-Java-Interview-Questions-9-320.jpg)
![Question 32:
public class Test
{
public static void main(String[] args)
{
Integer a = 1000, b = 1000;
System.out.println(a == b);
Integer c = 100, d = 100;
System.out.println(c == d);
}
}
why does the first case print false while the
second case prints true?](https://image.slidesharecdn.com/37-java-interview-questions-160126092321/85/37-Java-Interview-Questions-33-320.jpg)
37 Java Interview Questions
- 1. 37 Java Interview Practice Questions
- 2. What is the difference between String, StringBuffer, and StringBuilder in Java? Question 1:
- 3. How do you run a Java application on the command line and set the classpath with multiple jars? Question 2:
- 4. What is the difference between final, finalize, and finally? Question 3:
- 5. How does Garbage Collection prevent a Java application from going out of memory? Question 4:
- 6. What is the difference between a ClassNotFoundException a n d NoClassDefFoundError? Question 5:
- 7. Why isn't String's .length() accurate? Question 6:
- 8. Given two double values d1, d2, why isn’t it reliable to test their equality using: Question 7: d1 == d2
- 9. What is the problem with this code: Question 8: final byte[] bytes = someString.getBytes();
- 10. What is the JIT? Question 9:
- 11. final double d = 1 / 2; System.out.println(d); Question 10: Why does Print 0? How can you make the code print 0.5 instead?
- 12. IntStream.range(0, 10).forEach(System.out::println); Question 11: In this code: what is the inferred type of the method reference System.out::println?
- 13. final Path path = Paths.get(...); Files.lines(path).forEach(System.out::println); Question 12: What is the problem with this code:
- 14. What will be the contents of the list after this operation and why? Question 13: final List<Integer> list = new ArrayList<>(); list.add(1); list.add(2); list.add(3); list.remove(2);
- 15. Write a function to detect if two strings are anagrams (for example, SAVE and VASE) Question 14:
- 16. What is the contract between equals and hashCode of an object? Question 15:
- 17. Can an enum be extended? Question 16:
- 18. How threadsafe is enum in Java? Question 17:
- 19. How does a JVM handle storing local variables vs storing objects? Question 18:
- 20. Identify the problem in the following code: Question 19: public class Foo { public Foo() { doSomething(); } public void doSomething() { System.out.println("do something acceptable"); } } public class Bar extends Foo { public void doSomething() { System.out.println("yolo"); Zoom zoom = new Zoom(this); } }
- 21. When do you use volatile variables? Question 20:
- 22. Why do you need to use synchronized methods or blocks? Question 21:
- 23. What is the difference between HashMap and ConcurrentHashMap? Question 22:
- 24. When do you need to override the equals and hashCode methods in Java? Question 23:
- 25. What is a service? Question 24:
- 26. What is a good usecase of calling System.gc()? Question 25:
- 27. What is the marker interface in Java? Question 26:
- 28. How are Annotations better than a Marker Interfaces? Question 27:
- 29. What are checked and unchecked exceptions? When do you use them? Question 28:
- 30. int a = 1L; Won’t compile and int b = 0; b += 1L; compiles fine. Why ? Question 29:
- 31. Why aren’t you allowed to extend more than one class in Java but are allowed to implement multiple interfaces? Question 30:
- 32. Question 31: Test t = null; t.someMethod(); public static void someMethod() { ... } Why doesn’t the following code generate a NullPointerException even when the instance is null?
- 33. Question 32: public class Test { public static void main(String[] args) { Integer a = 1000, b = 1000; System.out.println(a == b); Integer c = 100, d = 100; System.out.println(c == d); } } why does the first case print false while the second case prints true?
- 34. Question 33: String s1="home"; String s2="mohe"; How do you check whether or not the following two strings are anagrams?
- 35. How do you reverse String("Java Programming") without using Iterations and Recursions? Question 34:
- 36. Give real world examples of when to use an ArrayList and when to use LinkedList Question 35:
- 37. What is the difference between an Iterator and a ListIterator? Question 36:
- 38. What is the advantage of a generic collection? Question 37:
- 39. Did you know how to answer all 37 questions? Feel free to check your answers here or schedule a mock interview with an experienced Java developer